The present invention relates to a coated ion exchange material suitable for use in chromatography medium, and a method of forming this material.
In one form of liquid chromatography, columns are packed with a discrete organic polymer granule or particle medium having functionally active surfaces. Materials for performing liquid chromatography are known where only thin outer surfaces of the chromatographic support materials are available for active exchange of ions with liquid media. For example, Small, et al. U.S. Pat. No. 4,101,460 describes an ion exchange composition comprising Component A, an insoluble synthetic resin substrate having ion-exchanging sites on its available surface, and Component B, a finely divided insoluble material, irreversibly attached thereto by electrostatic forces. Component B is typically deposited onto Component A from a latex.
A disadvantage regarding the latex coating procedure is that it can take a substantial period of time, e.g., days or even weeks, to make an optimized packed column. Such procedures typically require applying the coating after the column is packed which increases the manufacturing time and labor compared to synthetic methods which can provide a finished product prior to packing. This is because the packing can be made more efficiently in large batches rather than on a column-by-column basis. Also, latex synthesis is generally limited to water insoluble monomers, significantly limiting the choice of available monomers.
Other particulate bed materials with ion exchange layering particles irreversibly bound to the outer surface of support particles are described in Barretto, U.S. Pat. No. 5,532,279. In one embodiment, Barretto describes forming a complex by contacting a suitable dispersant with monomer in an aqueous solution in which the monomer is insoluble. Under suitable conditions for suspension polymerization, the monomer will polymerize to form resin support particles having a dispersant irreversibly attached to those particles. Fine synthetic layering particles are bound to the support particles. A number of other embodiments are disclosed for irreversible attachment.
Another form of ion chromatographic medium is made by forming a coating by binding a solution of a preformed polymer with saturated carbon chain backbones including leaving groups under hydrogen abstraction conditions to bind to preformed polymer to a substrate in the presence of a free-radical catalyst which removes leaving groups from the carbon chain to form the covalent bonds. See Srinivasan, U.S. Pat. No. 6,074,541. This coating is disclosed for use with a variety of substrates including the inner wall of a conduit or particles for use in a packed bed.
A significant application of ion chromatography is in analyzing water, e.g., surface water and well water. Worldwide, municipal facilities use ion chromatography to qualify water as being appropriate for human consumption. The ionic content of water varies significantly depending on the source, storage and handling conditions. In samples containing high levels of matrix ions such as chloride, sulfate and bicarbonate detecting trace amounts of ions such as bromate or chlorite or perchlorate is challenging.
Methods for ion analysis of water include direct injection and analysis, or pretreating the samples prior to a direct injection analysis. Direct injection is preferred, however, application of this method is limited for some samples with high matrix content due to the limited capacity of the stationary phases currently available. An alternate approach is to pursue pre-concentration of the ions in the sample in conjunction with heart cutting or some means of removing the matrix ions prior to analysis. Heart cutting methods are two-dimensional methods in which the matrix ions are separated or removed in the first dimension, enabling analysis of the ions of interest. Matrix ions are also removed using sample pretreatment with one or more pretreatment cartridges. For example a barium form cation exchange resin based cartridge is used to remove sulfate from the sample matrix. The methods discussed above are multi-step processes with multiple valve configurations, complex plumbing or are labor intensive. Therefore it is desirable to simplify the analysis protocol for samples containing matrix ions. Ion exchange phases having unique enhanced capacity architecture will facilitate analysis.
To counter some of the limitations of existing stationary phases a new phase and method of making this phase was recently introduced (U.S. Pat. No. 7,291,395). The method and phase rely on an amine epoxide-based chemistry to grow a hydrophilic hyperbranched structure on top of the substrate of the ion exchange phase. This type of structure does not have the limitation of inter-penetrating polymers of the prior art phases and shows excellent efficiencies. The capacity of these phases, however, could be enhanced to facilitate direct injection of samples with high matrix ion concentration.
High capacity ion exchange phases should provide high resolution of species of interest, particularly over matrix ions, and the ability to handle high matrix ion concentrations without over-loading the stationary phase. These phases should also allow quantitation at trace levels of ions other than matrix ions and have unique selectivity to facilitate separation of species of interest. Furthermore, a desirable ion exchange material will be resistant to binding matrix ions, preventing these ions from interacting with the stationary phase and decreasing available capacity of this phase. The present invention provides such high capacity stationary phases and methods of making and using them.